The present invention relates to a fluorine-containing copolymer which is capable of chemical curing, and a curable composition containing the copolymer.
A copolymer of a fluoroolefin and ethylene has generally excellent properties such as weatherability, heat resistance and chemical resistance, and is applied to various uses. The copolymer is, however, poor in solubility to usual organic solvents. When being soluble, kinds and conditions of usable solvents are severely restricted. Further, since the copolymer has a high crystallinity, there are problems in optical properties such as glossiness and transparency. A copolymer is prepared by employing isobutylene instead of ethylene and incorporating a copolymerizable monomer (Japanese Examined Patent Publication No. 16152/1968). Though the copolymer is relatively soluble in usual organic solvents and is excellent in weatherability, the kinds of usable solvents are not yet enough. In addition, the copolymer does not have a reactive functional group, and thus cannot be cured by chemical reaction.
Recently, researchers have studied fluorocarbon resin paints which are curable at room temperature without baking at an elevated temperature. For example, Japanese Examined Patent Publication No. 21686/1985 discloses that a fluorine-containing copolymer prepared by copolymerizing a fluoroolefin, vinyl ethers and a hydroxyalkyl vinyl ether is useful as a curable paint at room temperature having weatherability. However, since the copolymer contains various vinyl monomers at an amount of approximately 50% by mole as a monomer unit, there are problems in weatherability and also in stain resistance.
As described above, the conventional fluorine-containing copolymers have both merits and demerits. As a result of the present inventors' intensive study for obtaining a polymer which is usable for a curable fluorocarbon resin paint with a usual solvent and can give a coating film being excellent in various properties such as weatherability, stain resistance, heat-yellowing resistance and optical properties, the inventors have found the fact that the above objects can be accomplished by using a fluorine containing copolymer prepared by polymerizing the fluoroolefins, the .beta.-methyl substituted .alpha.-olefin, the monomers having a chemically curable functional group and the monomers having an ester moiety in the side chains, if necessary, a monomer having carboxyl groups and/or the other copolymerizable monomers, and then the present invention has been completed.